The use of parabolic aluminized reflector (PAR), elliptical reflector (ER), or reflector (R) lamps for general spot, downlighting, and/or flood lighting applications is well established. In particular, R, PAR, and ER type lamps have been accepted as the lamps of choice for short to medium distance outdoor uses, as well as for indoor display, decoration, accent, and inspection applications of down lighting.
Traditionally, incandescent PAR-type lamps, particularly Sylvania's PAR38, have used a filament mounted transversely in the reflector, that is, perpendicular to its axis of symmetry, because this was the simplest configuration to manufacture.
The result of this configuration is an asymmetric beam pattern and the spreading of stray light outside of the useful beam. Additionally, the necessity of maintaining the proper atmosphere in the outer jacket required that the lamp be hermetically sealed with the lens flame-sealed to the reflector.
With the introduction of Sylvania's Capsylite PAR lamps, which use a halogen capsule as a light source, came lamps with axially mounted filaments which yield a more symmetric beam pattern and more efficient collection of light by the reflector into a useful beam.
Part of this gain in optical efficiency is due to the fact that the Capsylite lamps use a compact filament which more nearly approaches the theoretically ideal "point" source.
In Capsylite lamps operating under United States type electrical systems (i.e., 120-130 V; 60 Hertz) such compact filaments are made possible by the use of a halfwave rectifying diode which effectively reduces the capsule voltage from 120 V to about 84 V. Furthermore, since the atmosphere in the outer envelope is no longer critical because of the capsule, the lamp need not be hermetic and bonded beam lamps have appeared.
In European line voltage PAR lamps, typically of 220 to 250 V, halogen capsules have not been used because of the exceedingly fine wire that is required at this high voltage.
Low voltage (.ltoreq.150 W), line voltage filaments tend to be long and flimsy, prone to sag and requiring multiple supports which reduce efficiency. Voltage reducing diodes cannot be used because they produce objectionable flickering of the filament when run on the 50 cycle AC which is standard in Europe.
"Folded" filaments tend to have detrimental interactions between adjacent sections of the filament which will reduce life.
Coiled filaments are known, see for example, U.S. Pat. Nos. 1,180,159; 1,247,068; 2,142,865; 2,306,925; 2,774,918; 4,208,609; and 4,316,116. However, none of these coiled filaments provides the unique features of the filament of the present invention.
Filament supports are also known, see for example, U.S. Pat. Nos. 4,359,665; 4,208,606; 3,708,333; 3,736,455; 3,678,319; 3,634,722; 3,335,312; and 3,173,051. However, previously employed filament supports typically caused problems in terms of shadowing and/or scattering of light.
While quartz halogen capsules in the 220-250 V range have been made, they are generally inefficient and complicated affairs with "zig-zagged" filaments and multiple coil supports.
Thus, conventional quartz capsules and the typical filaments and/or supports usually associated therewith, are not well suited for use in PAR lamps since they are lacking both in luminous efficiency and in optical efficiency, they are also more expensive to produce than hard glass capsules due to the high cost of materials and processes involved and the amount of labor required.
The present invention overcomes the difficulties mentioned above with respect to European type PAR and A-Line lamps by providing a unique filament and non-interfering supports therefore.